Detecting RNA base methylations in single cells by in situ hybridization.

Methylated bases in tRNA, rRNA and mRNA control a variety of cellular processes, including protein synthesis, antimicrobial resistance and gene expression. Currently, bulk methods that report the average methylation state of ~104-107 cells are used to detect these modifications, obscuring potentially important biological information. Here, we use in situ hybridization of Molecular Beacons for single-cell detection of three methylations (m62A, m1G and m3U) that destabilize Watson-Crick base pairs. Our method-methylation-sensitive RNA fluorescence in situ hybridization-detects single methylations of rRNA, quantifies antibiotic-resistant bacteria in mixtures of cells and simultaneously detects multiple methylations using multicolor fluorescence imaging.

Individual aggregates of amyloid beta induce temporary calcium influx through the cell membrane of neuronal cells.

Local delivery of amyloid beta oligomers from the tip of a nanopipette, controlled over the cell surface, has been used to deliver physiological picomolar oligomer concentrations to primary astrocytes or neurons. Calcium influx was observed when as few as 2000 oligomers were delivered to the cell surface. When the dosing of oligomers was stopped the intracellular calcium returned to basal levels or below. Calcium influx was prevented by the presence in the pipette of the extracellular chaperone clusterin, which is known to selectively bind oligomers, and by the presence a specific nanobody to amyloid beta. These data are consistent with individual oligomers larger than trimers inducing calcium entry as they cross the cell membrane, a result supported by imaging experiments in bilayers, and suggest that the initial molecular event that leads to neuronal damage does not involve any cellular receptors, in contrast to work performed at much higher oligomer concentrations.

A mechanistic model of tau amyloid aggregation based on direct observation of oligomers.

Protein aggregation plays a key role in neurodegenerative disease, giving rise to small oligomers that may become cytotoxic to cells. The fundamental microscopic reactions taking place during aggregation, and their rate constants, have been difficult to determine due to lack of suitable methods to identify and follow the low concentration of oligomers over time. Here we use single-molecule fluorescence to study the aggregation of the repeat domain of tau (K18), and two mutant forms linked with familial frontotemporal dementia, the deletion mutant ΔK280 and the point mutant P301L. Our kinetic analysis reveals that aggregation proceeds via monomeric assembly into small oligomers, and a subsequent slow structural conversion step before fibril formation. Using this approach, we have been able to quantitatively determine how these mutations alter the aggregation energy landscape.

Inhibition of Ih reduces epileptiform activity in rodent hippocampal slices.

Hyperpolarization-activated cyclic nucleotide gated (HCN) ion channels regulate membrane potential, neurotransmitter release, and patterning of synchronized neuronal activity. Currently, there is an intense debate as to whether or not these ion channels play a pro- or anticonvulsant role in vivo. To gain an insight into this question, we have examined how inhibitors of the response mediated by HCN channels (referred to as I(h)) affect epileptiform activity induced in adult hippocampal slices. The archetypal I(h) blocker ZD-7288 produced a concentration-dependent inhibition of both nonsynaptic- (low Ca(2+)/elevated K(+) aCSF) and synaptic- (low Mg(2+) aCSF, elevated K(+) aCSF or convulsant application (bicuculline or pentylenetetrazol)) based epileptiform activities. The IC(50) value for ZD-7288 induced inhibition of epileptiform activity was similar across all forms of epileptiform response and was below concentrations producing nonspecific inhibition of glutamatergic synaptic transmission. Furthermore, capsazepine, which exhibits similar potency to ZD-7288 at inhibiting I(h), failed to inhibit glutamatergic synaptic transmission per se but produced a significant inhibition of bicuculline-induced epileptiform activity. These data suggest that broad spectrum inhibition of I(h) reduces neuronal hyperexcitability in the hippocampus.